1. Field of the Invention
The present invention relates to a peer-to-peer communications system configured to enable pieces of terminal equipment to connect directly with each other, transfer data, and share information, as well as to terminal equipment constituting the communications system.
2. Description of the Related Art
A communications system of client-server type suffers a problem of heavy load being imposed on a server as a result of concentration of communication on the server. In order to solve this problem, attention has been paid to peer-to-peer communication by means of which pieces of terminal equipment communicate with each other.
Incidentally, a security problem of a network has emerged, and a device (hereinafter described as “NAT/Firewall”) having the function of rejecting direct connection with subordinate devices from the outside, such as an NAT (Network Address Translation) or a firewall, is often interposed between the Internet and the piece of terminal equipment. However, when the NAT/Firewall is present, a piece of terminal equipment belonging to a network (hereinafter described as a “private network”) located inside of the NAT/firewall can transfer data directly to a piece of terminal equipment located outside the NAT/Firewall, but the piece of terminal equipment located outside the NAT/Firewall cannot transfer data directly to the terminal equipment located within the private network (see FIG. 3). Pieces of terminal equipment located outside of the NAT/Firewall are assigned globally-unique global addresses, whereas pieces of terminal equipment located within the private network are assigned private addresses which are unique within the private network but might include overlaps from the worldwide viewpoint. Therefore, the pieces of terminal equipment located outside the private network cannot specify an address of the terminal equipment belonging to the private network. Therefore, it has been impossible to establish a peer-to-peer communications system which enables the pieces of terminal equipment located inside and outside the private network to directly transfer data or share information.
In order to solve the problem, there has been proposed a system which enables direct transfer of data from a piece of terminal equipment having a global address to a piece of terminal equipment having a private address by means of setting up a repeating installation (a communications control server) having a global address in the network outside of the private network. In this conventional system, all pieces of terminal equipment connect to the repeating installation, to thus acquire session information about themselves, such as data transfer requests, regardless of whether they are outside of or belong to a private network. After acquisition of the session information about themselves, the pieces of terminal equipment directly transfer data in accordance with the information while bypassing the communications control server (see JP-A-2003-101590).